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It pays to know the parasites you’re dealing with in order to pick the right dewormer to control them.
“One of the key components to any deworming program has to be a fecal egg count reduction test (FECRT),” Newcomb says. “The FECRT is the only way at present for the producer to monitor the efficacy of his deworming program. Since no two operations are alike, every producer should work with their veterinarian or cattle parasitologist to develop a deworming program that meets the specific needs and goals of their operation.”
The FECRT is a herd-level test, points out Roberto Cortinas, DVM and assistant professor in the University of Nebraska Lincoln (UNL) School of Veterinary Medicine and Biomedical Sciences. “At least 25 animals should be randomly sampled, preferably from the same age class, before and after deworming. You don’t have to sample the same individuals – you’re sampling the herd for overall reduction in egg production.”
A Closer Look: Controlling Parasites Doubly Important In Time Of Drought
Bonds says their stockers are dewormed upon arrival, either with an injectible or a pour-on. If needed, a second treatment is given 30-60 days later.
“We determine whether a second or third treatment is needed by collecting fecal samples,” she says. “We also read reports of different regions and pastures with our drug rep. We can see which pastures will require cattle to be dewormed and which one doesn’t.”
Woodruff says fecal egg counts (FEC) are a widely used method of evaluating internal parasite infestation. “FEC is performed by mixing a known volume of feces with either a saturated salt or sugar solution, allowing parasite eggs to float to the surface where they can be captured on a microscope slide,” he says.
Parasite eggs can then be evaluated and counted. FEC results are normally reported as eggs per 1 gram of feces, Woodruff says, adding that “misunderstandings about the level of parasite infestation occur with FEC results reported as eggs per 3 grams, or eggs per 5 grams, of feces.”
FEC is relatively inexpensive and easy to accomplish. But another process called “coproculture” identifies specific internal parasites present. “Coproculture is performed by incubating the fecal sample for 2-3 weeks and allowing eggs to hatch into larvae,” Woodruff says. “The larvae can then be classified as to genus and species.
“Knowledge of which species of parasites are present is important, since some internal parasites are considered more pathogenic than others, and some are more proficient egg producers. Coproculture results aid in tailoring a dewormer program specific to the family of parasites present in a group of animals.”
A follow-up FEC determines the effectiveness of initial dewormer applications, he says. It normally involves testing of two fecal samples from the same animal, collected 10-14 days apart. A calculation can then be made as to the percent of reduction in internal parasite eggs.
Cortinas adds that UNL’s Veterinary Diagnostic Laboratory is in the process of instituting a polymerase chain reaction (PCR) test that will provide quicker results than coproculture. “It can be done right when we do the fecal exam without having to wait for the eggs to hatch, which can take 1-2 weeks,” he says. Colorado State University also offers the PCR test.
Woodruff says timing of the follow-up sample is important to accurately assess effectiveness of a parasite control product. “Adult parasites not removed by treatment may suspend shedding eggs for several days after exposure to the treatment drug, thus artificially underestimating remaining parasite levels,” he says.
“If the second sample is collected much past three weeks post-treatment, it could possess eggs from newly acquired infestations. There could be egg-shedding variations due to diet change effects on the adult worm; or in the case of inhibited Ostertagi, a new crop of larvae may have developed into mature, egg-laying adults.”
Bonds says her operation virtually always takes an FEC when a pour-on is used. “Also, we like using pour-ons when flies are an exceptional problem,” she adds. “We see some extra fly control.”
Mustian says producers and stocker operators should also consult their vet and animal health reps to look for Cooperia worms. “In wet, low-lying areas, you also need to look at liver flukes,” he adds.
Mustian notes that in some parasite control programs, three applications may be needed. “If you’re going by the book, there should be two applications – one in late spring or early summer, and one in the fall near November,” he says. “If you spend the money on a good deworming program, it may pay you back 3-4 times over.
“It’s not only important for gain, but for animal health. If cattle have a heavy worm load, they don’t respond as well to a vaccine,” he says.